مدیریت تحرک در شبکه های بی سیم ترکیبی: روند ها و چالش ها

Future generation wireless networks are envisioned to be a combination of diverse but complementary access technologies. Internetworking these types of networks will provide mobile users with ubiquitous connectivity across a wide range of networking environments. The integration of existing and emerging heterogeneous wireless networks requires the design of intelligent handoff and location management schemes to enable mobile users to switch network access and experience uninterrupted service continuity anywhere, anytime. Real deployment of such mobility strategies remains a significant challenge. In this article, we focus on handoff management. We discuss in detail handoff decision and implementation procedures and present recent handoff techniques that aim at providing mobility over a wide range of access technologies. We also discuss some of the capabilities of mobile terminals that are necessary to implement seamless mobility over hybrid wireless networks. Furthermore, we also present and discuss limitations of recent handoff design architectures and protocols as well as outstanding challenges that still need to be addressed to achieve portable and scalable handoff solutions for continuous connectivity across wireless access networks.

Mobile wireless technology has gained tremendous popularity due to its ability to provide ubiquitous information access to users on the move. However, presently, there is no single wireless network technology that is capable of simultaneously providing a low latency, high bandwidth, and wide area data service to a large number of mobile users. Wireless Overlay Networks [1]—a hierarchical structure of room-size, building-size, and wide area data networks solve the problem of providing network connectivity to a large number of moving consumers in an efficient and scalable way. In an overlay network, lower levels are comprised of high bandwidth wireless cells that provide a small coverage area. Higher levels in the hierarchy provide a lower bandwidth but a much wider access network. A mobile device with multiple wireless network interfaces can access these networks as it moves between different network environments. Next generation wireless systems typically constitute different types of access technologies [15]. The heterogeneity that will characterize future wireless systems instigates the development of intelligent and efficient handoff management mechanisms that can provide seamless roaming capability to end-users moving between several different access networks.

In this article, we have presented a detailed discussion of various components of handoff management as well as recent handoff techniques for mobility across heterogeneous wireless access networks. We have also discussed about various features of multimodal mobile terminals that will enable the deployment of efficient mobility solutions. We have presented several handoff implementation issues and challenges that still need to be addressed to allow seamless mobility in future radio access systems. We found that current roaming techniques are not well suited to support continuity of application sessions in heterogeneous mobile environments. Extensive research and technological improvements in the areas of radio transmission, mobility management, and implementation of multimodal devices will lead to the development of an adaptable network environment where users will be able to use self-configuring devices that will enable them to realize seamless global roaming efficiently and cost-effectively. These systems are expected to provide users the ability to execute various mobile multimedia applications while moving across different types of networks environments. Work is in progress to migrate the existing networks to an optimized system in which several different types of technologies can interoperate and co-exist in a way so as to provide a completely seamless mobility experience to end-users.